1. Field of the invention
The present invention is related to minimally invasive devices and methods used in laser treatments. More particularly, the invention relates to lithotripsy techniques based on laser radiation.
2. Invention Disclosure Statement
Calculi or stones are the result of a concretion of material, usually mineral salts that form in an organ or duct of the body. They cause a number of important medical conditions by several mechanisms:                Irritation of nearby tissues, causing pain, swelling, and inflammation.        Obstruction of an opening or duct, interfering with normal flow and disrupting the function of the organ in question.        Predisposition to infection due to disruption of normal flow.        
The most common types are kidney stones, also called renal calculi, which are present within the urinary tract, mainly the kidneys or bladder and gallstones which develop in the gallbladder.
There are several approaches used in medicine for treating stones. Many calculi in the upper urinary tract are treated with extracorporeal shock-wave lithotripsy (ESWL). ESWL attempts to break up the stone by using an externally-applied, focused, high-intensity mechanical (acoustic) pulse. Extracorporeal lithotripsy works best with stones of small diameter. For those stones that are poor candidates for this modality, endoscopic therapy is indicated. Endoscopic lithotripsy refers to the visualization of a calculus and the simultaneous application of a form of energy to fragment a stone into either extractable or passable pieces. Ureteroscopy is the most common means of visualizing an upper urinary tract calculus. Alternatively, percutaneous techniques also can be used on kidney stones.
Energy sources used in Endoscopic lithotripters include ultrasonic, electrohydraulic, and mechanical devices, as well as various lasers.
Laser lithotripsy was first introduced commercially in the late 1980s, based on the fact that pulsed light energy, delivered via an optical fiber, is converted into mechanical energy in the form of a cavitation bubble associated with the occurrence of shock-waves. This mechanical energy is responsible for the destruction of calculi. It is a procedure underpinned by plasma formation on the surface of stones to be shattered. Through very thin optical fibers, laser impulses are transmitted to the stone surface with high peak power radiation. If stones or the surrounding liquid absorb the radiation and the power density exceeds a certain threshold, plasma formation occurs. The plasma, created by an ionization with rapid growth of the matter, produces sparkler bubbles associated with cavitation and the shock waves effect. The plasma and cavitation phenomena are associated with strong photo and thermo-ablative effects; plasma bubbles have inside temperatures of several thousand of degrees, and the presence of cavitation effects is associated with a typical noise produced by the shock waves.
First laser used was a pulsed-dye laser, emitting at 504 nm of light delivered through optical quartz fibers. This was a nonthermal laser that produced plasma between the tip of the fiber and the calculus, fragmenting stone with a photo acoustic effect. As an example, in U.S. Pat. No. 5,071,422, Watson et al. disclose a method to treat calculi, stones and calcified tissue with a pulsed-dye laser. But if dye laser radiation is not absorbed by stones, plasma formation will not occur and laser lithotripsy will not be effective. Since a pulsed dye laser source is used, frequent maintenance is often required as this source is not a solid-state laser.
As an alternative, Alexandrite lasers have been used for lithotripsy, emitting with very short pulse duration. For instance, in U.S. Pat. No. 5,009,658, Damgaard-Iversen et al. disclose a dual frequency laser lithotripter, which emits at two different wavelengths obtained from an Alexandrite laser. The usage of this kind of lasers has rendered poor results due to the unfavorable absorption at its wavelength range.
Nd:YAG lasers have been used obtaining some good results. As an example, in U.S. Pat. No. 4,960,108, Reichel uses a metal compound rinsing liquid, which is delivered around the target stone and irradiated with a Nd:YAG laser. However, this technology lacks precision compared to other laser technologies. With the need to use high peak powers, another drawback is that the distal end of the fiber may be damaged if it makes contact with the stone.
In an attempt to overcome some of these disadvantages, holmium:YAG lasers emerged, which are thermal lasers using 2150 nm wavelength. The energy is delivered through low-water density quartz fibers. For example, Hoang discloses in U.S. Pat. No. 5,860,972 a method for detection and destruction of urinary calculi using a Ho:YAG laser. These lasers have more precision and are more effective than previously mentioned technologies. However, one important drawback of this laser is that the energy produced has equally powerful effects on stones and soft tissues. Furthermore, size and cost are important issues to take into account. Diode lasers have numerous advantages over ionic crystal lasers. Among them, higher output, at reduced dimensions and weight. They also have simpler and smaller air cooling systems. Moreover, being integrated with optical fibers, they have a high reliability and do not need alignment.
When applying previous state of the art laser lithotripsy techniques, the successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone, which fragment the stones into smaller pieces that then can easily pass through the ureters or the cystic duct. The process may take about an hour. This can be tiresome and stressful for both physician and patient. Present invention can successfully fragment stones more effectively therefore reducing the duration of the intervention.
Due to the disadvantages and deficiencies of current lithotripsy techniques, a need exists for a device that provides a fast, safe and more economical alternative to address their shortcomings.